The present invention is related to fine denier polyester fibers. In particular, the invention is related to fine denier polyester fibers obtained by splitting multi-component polyester fibers and to fabrics made from such fine fibers.
Polyester has long been recognized as a desirable material for textile applications. Polyester fibers are readily formed into woven, knit, and nonwoven fabrics. Polyester fabrics are particularly attractive because they are economical, resilient, insensitive to moisture, and have superior tensile properties. It is further known that use of very fine denier polyester fibers produces a softer fabric, among other benefits. As would be expected, softness is considered to be a highly beneficial attribute in apparel applications.
Melt extrusion processes for spinning continuous filament and spunbond filaments from thermoplastic resins such as polyester are well known in the art. Meltblown processes are also known for spinning thermoplastic resins into fiber, in particular fine denier fiber. In general, melt extrusion processes provide higher strength fibers than microfibers produced using meltblown methods, which impart less orientation to the polymer and employ a lower molecular weight resin. However, it is difficult to produce fine denier fibers, in particular fibers of 2 denier or less, using conventional melt extrusion processes.
One avenue by which to overcome this difficulty is to split multicomponent continuous filament or staple fiber into fine denier filaments, or microfilaments, in which each fine denier filament has only one polymer component. It is now widely known that multicomponent fiber, also referred to as composite fiber, may be split into fine fibers comprised of the respective components, if the composite fiber is formed from polymers which are incompatible in some respect. The single composite filament thus becomes a bundle of individual component microfilaments.
Typical known splittable multicomponent fibers containing polyester include the polyester/nylon fibers described in U.S. Pat. Nos. 4,239,720, 4,118,534, and 4,364,983. Composite splittable polyester/olefin fibers are likewise described in U.S. Pat. No. 5,783,503. Tricomponent dividable fibers containing polyester are taught in U.S. Pat. No. 4,663,221.
A number of processes are known for separating fine denier filaments from multicomponent fibers. The particular process employed depends upon the specific combination of components comprising the fiber, as well as their configuration.
A common process by which to divide a multicomponent fiber involves mechanically working the fiber. Methods commonly employed to work the fiber include drawing on godet rolls, beating or carding. It is also known that fabric formation processes such as needle punching or hydroentangling may supply sufficient energy to a multicomponent fiber to effect separation. When mechanical action is used to separate multicomponent fibers, the fiber components must be selected to bond poorly with each other to facilitate subsequent separation. In that vein, conventional opinion has been that the polymer components must differ from each other significantly to ensure minimal interfilamentary bonding. It is for this reason that polymers having disparate chemistries, i.e., from different chemical families, have been chosen as components for mechanically dissociable composite fibers to date.
However, the use of such disparate chemistries is problematic, as polymers from different chemical families accept and retain dyestuffs differently. As an example, a nylon/polyester multicomponent fiber would typically be dyed using two dyestuffs, an acid dye for the nylon component and a disperse dye for the polyester component. Typically, the dye processes required for these dyestuffs are quite different, introducing process inefficiencies. In addition, it is extraordinarily difficult to match the color imparted to the respective components using differing dyes. This dyeing phenomenon is noted in U.S. Pat. No. 4,118,534, in which a nylon/copolyester multicomponent fiber was dyed with the xe2x80x9csame colorxe2x80x9d acid and cationic dyes for the nylon and copolyester components, respectively. The dyes produced different colors on their respective microfilaments, giving rise to a xe2x80x9chaloxe2x80x9d effect.
Currently, to produce fine denier fabrics having uniform color, a multicomponent fiber comprised of a desired polymer and a soluble polymer is formed. The soluble polymer is then dissolved out of the composite fiber, leaving the desired microfilaments to be dyed. U.S. Pat. No. 5,593,778 utilizes such a process, in which a poly(lactic acid) copolymer component is dissolved away, thereby providing fine denier copolyester filaments. A comparable process is given in U.S. Pat. No. 4,663,221, in which a matrix component is dissolved away using a solvent such as toluene, to yield a fiber bundle comprised of polyurethane and polyester microfilaments. U.S. Pat. No. 5,162,074 also describes this method in general terms, recommending the use of polystyrene as a soluble component in the production of fine denier filaments. In general, polystyrene is soluble in hydrocarbon solvents, such as toluene.
The use of dissolvable matrixes to produce fine denier filaments is problematic. First, the manufacturing yields are inherently low because a significant portion of the multiconstituent fiber must be destroyed to produce the microfilaments. Secondly, the wastewater or spent hydrocarbon solvent generated by such processes poses an environmental issue. Third, the time required to dissolve the matrix component out of the composite fiber further exacerbates manufacturing inefficiencies.
Based on the foregoing, although a number of methods for splitting multicomponent fibers to obtain fine denier filaments are known, there is still need for improvement.
The present invention provides splittable multicomponent fibers and fiber bundles which include a plurality of fine denier filaments having many varied applications in the textile and industrial sector. The fibers can exhibit many advantageous properties, such as a soft, silk-like hand, high covering power, and the like. Further the fiber bundles can be uniformly dyeable. The present invention further provides fabrics formed of the multicomponent fibers and fiber bundles, as well as an economical, environmentally friendly process by which to produce fine denier polyester filaments.
In particular, the invention provides mechanically divisible or splittable fibers formed of polyester components. The fibers can have a variety of configurations, including pie/wedge fibers, segmented round fibers, segmented oval fibers, segmented rectangular fibers, segmented ribbon fibers, and segmented multilobal fibers. Further, the mechanically splittable multicomponent fibers can be in the form of continuous filaments, staple fibers, or meltblown fibers. The splittable fibers may be dissociated by a variety of mechanical actions, such as impinging with high pressure water, carding, crimping, drawing, and the like.
In one particularly advantageous aspect of the invention, the divisible multicomponent fiber includes at least one aliphatic polyester component, advantageously poly(lactic acid), and at least one aromatic polyester component. The polymer components are dissociable by mechanical means to form a bundle of fine denier polyester fibers. A particularly advantageous embodiment is a splittable multicomponent fiber formed of equal parts of poly(lactic acid) and poly(ethylene terephthalate) in a pie/wedge configuration.
The instant invention also provides a fiber bundle which includes a plurality of dissociated polyester microfibers of different polyester compositions. Specifically the fiber bundle include a plurality of aliphatic polyester microfilaments, advantageously poly(lactic acid) microfilaments, and aromatic polyester microfilaments. In general, the microfilaments of the present invention range in size from 0.05 to 1.5 denier.
The multicomponent fibers can be formed into a variety of textile structures, including nonwoven webs, either prior to or after fiber dissociation. Fabrics made using the fine denier fibers of the present invention are both economical to produce and behave in important ways as fabrics made entirely of polyester. As noted previously, earlier fabrics containing mechanically splittable composite filaments were based on disparate component chemistries. A typical conventional fabric produced from mechanically splittable composite fibers includes nylon and poly(ethylene terephthalate) microfilaments. As noted previously, such fabric must be dyed with one dye for the polyester microfilaments and a second dye for the nylon microfilaments. Often, this would require two separate dyeing processes, and it is very difficult to match the shade of the two fine denier fibers.
However, previous attempts to overcome this difficulty by making mechanically splittable fibers from pairs of polyesters have failed, because most polyesters have too high an affinity for each other to allow the segments to be split easily. Surprisingly, the inventors have found that an aliphatic polyester polymer, advantageously poly(lactic acid), can be made into an easily-splittable segmented fiber with aromatic polyesters, such as poly(ethylene terephthalate). The resulting composite fiber can be dyed with disperse dyes before or after splitting, thereby allowing a one-step xe2x80x9cunionxe2x80x9d dyeing. Union dyeing is a process in which the same color is imparted to different fibers contained in a fabric by means of a one bath process, thus providing fabric having a uniform color.
Another aspect of the invention teaches fabrics formed from mechanically splittable multicomponent fibers of poly(lactic acid) and aromatic polyester components, as well as the methods by which to produce such fabrics. In this aspect of the invention, the multicomponent fibers can be divided into microfilaments either prior to, during, or following fabric formation. Fabrics of the present invention may generally be formed by weaving, knitting, or nonwoven processes. Advantageously the fabric is a dry-laid nonwoven fabric formed from the multicomponent fibers of the present invention. Another advantageous fabric is a dry-laid nonwoven fabric bonded by hydroentangling.
Products comprising the fabric of the present invention provide further advantageous embodiments. Particularly preferred products include synthetic suede fabrics and filtration media.
By providing fiber bundles comprised entirely of fine denier polyester filaments, the present invention permits soft, uniformly dyeable fabrics having a high degree of coverage to be economically produced. In specific, the multiconstituent fibers of the present invention allow the production of fabrics containing fine denier polyester filaments which may be formed without hydrocarbon solvents or extraordinary waste, and which may be dyed to a uniform shade in a single dyeing operation.
Further understanding of the processes and systems of the invention will be understood with reference to the brief description of the drawings and detailed description which follows herein.